This invention relates to tear tape and more particularly to multilayer thermoplastic resin tear tapes, the method of making tear tape and to apparatus for and the method of embossing tear tape with indicia representative of information.
Tear tapes for opening packaging are well known. They are typically adhered to the packaging material with one end exposed. The tape may therefore be pulled to tear and open the packaging when desired.
Polypropylene is the material of choice for many tear tape applications. To adhere the polypropylene tear tape to packaging material, which often is also polypropylene, adhesives are typically utilized as coatings on the tear tape. In the past, lacquer has been coated on the tear tape and a solvent applied to activate the lacquer as the tear tape is applied to the packaging. Another system employed has been coating the tear tape with a wax which is heated to adhere the tear tape to the packaging. Pressure sensitive adhesives coated on the tear tape have also been employed. In yet another system, hot melt adhesive has been coated on both sides of the tear tape and is activated by heat resulting from activation of an ultrasonic transducer.
The application of coatings to the tear tape material, however, involves extra processing steps, the need to control coating stations and hazards resulting from exposed materials, particularly those involving flammable materials or noxious fumes. Tear tape with a pressure sensitive adhesive coating has required careful control of tear tape tension as it is unwound from a roll and, indeed, often is employed with a powered unwind station due to the tension resulting from drawing tape from a roll where the tape is contacted by an underlying coated layer of pressure sensitive adhesive.
Counterfeiting is also an issue in product manufacturing. Thus it is desirable that packaging be identified in a unique manner to indicate a source of genuine product. Additionally, quality control is enhanced when product packaging is uniquely identified.
In one aspect, the invention relates to an elongated tear tape of thermoplastic resin material coextruded with at least one outer layer comprising either a hot melt adhesive or a pressure sensitive adhesive.
In embodiments employing a hot melt adhesive, the tear tape comprises a plurality of, preferably, three coextruded layers of thermoplastic material monoaxially oriented in the longitudinal direction of the tape, the two outer layers each comprising thermoplastic material and the hot melt adhesive. The hot melt adhesive in the outer layers comprises up to 25% thereof and preferably from 5 to 15% and, in certain applications, preferably about 10% thereof. A preferred hot melt adhesive is an ethylene vinyl acetate based adhesive.
In embodiments of tape employing a pressure sensitive adhesive, the tear tape comprises two or three coextruded layers of thermoplastic material monoaxially oriented in the direction of the tape, one outer layer comprising the pressure sensitive adhesive. The pressure sensitive material in the one layer comprises up to 25% and, in most applications, from 5 to 10% of the thickness of the tape. A preferred pressure sensitive adhesive is a styrene-isoprene-styrene based adhesive. The other outer layer of the tape comprises thermoplastic material and a release agent, preferably an ultra high molecular weight silicone polymer. The silicone comprises from 0.1 to 5% of the other layer. In a three layer tape, the inner layer is thermoplastic resin material.
In another aspect the invention relates to the method of making the foregoing tear tapes by coextruding a layer of thermoplastic resin material with at least one outer layer comprising the hot melt or pressure sensitive adhesive. In preferred embodiments, the tear tape employing hot melt adhesive is coextruded in three layers with thermoplastic material and adhesive in the two outer layers. The tear tape with pressure sensitive adhesive is coextruded in two or three layers with the adhesive in one layer and, preferably, with the other outer layer comprising thermoplastic material and a release agent; if formed in three layers, the internal layer comprises thermoplastic material.
In another aspect the invention relates to apparatus for bonding the tear tape with hot melt adhesive to packaging material and for embossing indicia representative of information thereon. The apparatus comprises an ultrasonic transducer for heating the material and an anvil roll in close proximity thereto. Indicia are formed in relief on the roll aligned with the path of the tear tape as it moves with the packaging between the transducer and the roll where by energy generated by the transducer heats the tape and packaging causing them to be deformed into and to be embossed with the indicia. A flanged roll preferably guides the tape in its path. Preferably, also, the relief indicia in the roll have a depth of from 0.0005 to 0.005 inches, sufficiently deep to emboss the indicia on the tape but not so deep as to lose character definition.
In yet another aspect, the invention relates to the method of embossing indicia representative of information in the tear tape. The method comprises passing the tape over an anvil roll having the indicia formed in relief in the roll surface, sealing the tape to packaging material and causing the tape and packaging to deform into the indicia. The tape is preferably guided to the path of the indicia.
Advantageously, tear tape according to the invention requires no separate coating or coating step in its manufacture. The inclusion of adhesive in the tape speeds the rate of production relative to ultrasonic bonding without adhesive. Additionally, controlling tape tension as it is unwound is less critical when hot melt adhesive is utilized than when pressure sensitive adhesive coatings are utilized. The provision of hot melt adhesive in both sides of the tape assures proper bonding even when the tape is twisted from one side to the other. On the other hand, the provision of pressure sensitive adhesive in one side of the tape and a release agent in the other side of the tape, both renders control of tape tension less critical and avoids the need to heat the adhesive for its activation. Embossing information on the tear tape permits identification of source to enhance detection of counterfeit product.
Other objects, advantages and features of the invention will be apparent from the following description of preferred embodiments taken together with the accompanying drawings, in which: